The present invention relates to pearlescent pigments having silver-gray gloss and excellent brightness. The pigments are based on a platelet-like, i.e., platelet-shaped, substrate coated with titanium dioxide and additionally oxidic compounds of copper, aluminum, and/or zinc. The invention also relates to a process for producing the same.
Metal flakes are used as pigments in paint for outdoor use, especially for exterior coating of cars. Aluminum flakes, for example, are used as pigment to obtain a silver-gray color. However, metals, especially aluminum, are disadvantageous in aqueous lacquer because they are reactive in aqueous systems. Specifically, contact of these metals with water generates dangerous quantities of hydrogen. It is known that paints of this type also undergo changes in appearance when exposed to various weather conditions. Therefore, it is difficult to obtain coatings with reproducible attributes.
In order to avoid these disadvantages, the metal flakes can be coated with polymers as disclosed in EP-A-0 393 579 (corresponding to U.S. Pat. No. 5,039,343). However, if metal pigments are mixed with pigments having mica flakes as a substrate for water-based varnish, the coating can be destroyed by the sharp edges of the mica flakes, and hydrogen may be generated. Therefore, there exists a need for the replacement in these and other uses of conventional metallic pigments.